1. Field of the Invention
The present invention relates to a method and apparatus for allocating resources in a wireless communication system. More particularly, the present invention relates to a method and apparatus for allocating resources in a communication system using a persistent resource allocation scheme.
2. Description of the Related Art
Next-generation communication systems are developing to provide various high-speed, high-capacity services to Mobile Stations (MSs). A next-generation communication system includes an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system and a Mobile Worldwide Interoperability for Microwave Access (WiMAX) communication system. The Mobile WiMAX communication system is a communication system based on the IEEE 802.16 communication system.
With reference to FIG. 1, a description will now be made of a frame structure in an IEEE 802.16 communication system.
FIG. 1 is a diagram illustrating a frame structure in an IEEE 802.16 communication system.
As illustrated in FIG. 1, a frame 111 includes a DownLink (DL) subframe 113, a Transmit/Receive Transition Gap (TTG) interval 115, an UpLink (UL) subframe 117, and a Receive/Transmit Transition Gap (RTG) interval 119. A length of the frame 111 is tframe, a length of the DL subframe 113 is tDL_subframe, a length of the TTG interval 115 is tTTG, a length of the UL subframe 117 is tUL_subframe, and a length of the RTG interval 119 is rRTG.
The DL subframe 113 includes a preamble region 121, a Frame Control Header (FCH) region 123, a DL_MAP region 125, a UL_MAP region 127, and a DL data burst region 129. A synchronization signal, e.g., preamble signal, for synchronization acquisition between a signal transmission apparatus, e.g., a Base Station (BS), and a signal reception apparatus, e.g., an MS, is transmitted during the preamble region 121. Basic information on subchannels, ranging and a modulation scheme is transmitted during the FCH region 123. A DL_MAP message is transmitted during the DL_MAP region 125, and a UL_MAP message is transmitted during the UL_MAP region 127. The DL_MAP message includes a DL_MAP Information Element (IE) indicating information about the DL data burst region 129. The UL_MAP message includes a UL_MAP IE indicating information about a UL data burst region 133. DL data bursts are transmitted during the DL data burst region 129.
The UL subframe 117 includes a control region 131 and the UL data burst region 133. Although not separately illustrated in FIG. 1, the control region 131 includes a ranging region, a Channel Quality Indicator Channel (CQICH) region, an ACKnowledgment (ACK) channel (ACKCH) region, and a sounding region. The ranging region is a region during which an MS transmits a ranging code, and when performing an initial network entry operation, performing a handoff operation or requesting resource allocation, an MS transmits a ranging code through the ranging region according to its purpose. The CQICH region indicates a region during which an MS transmits its CQI, and the ACKCH region indicates a region during which an MS transmits its success/failure in reception of DL data bursts. A sounding signal for allowing an MS to perform UL channel estimation is transmitted during the sounding region.
As described in FIG. 1, the IEEE 802.16 communication system allocates resources to an MS to exchange DL and UL traffic data with it, and provides the resource allocation information to the MS using a resource allocation message. The resource allocation message can be a DL_MAP message or a UL_MAP message. A transmission period of the DL_MAP message and UL_MAP message is a frame period.
However, in the service where traffic data is periodically transmitted to an MS, for example, in Voice over Internet Protocol (VoIP) service, BS's transmitting a resource allocation message at every frame to transmit resource allocation information for the resources allocated to the corresponding MS may cause an unnecessary waste in resources. Therefore, when providing a service having a periodic traffic transmission period like the VoIP service, it is preferable to persistently allocate resources for the corresponding MS. A scheme of persistently allocating resources for a particular MS is referred to as a ‘persistent resource allocation scheme’. For convenience, the persistent resource allocation scheme will be referred to herein as a ‘circuit-mode resource allocation scheme’.
When using the circuit-mode resource allocation scheme, an MS, once it is allocated resources from a BS, can persistently use the allocated resources without receiving the resource allocation message at every frame. Of course, when the resource allocation for the MS is changed or released, the BS can notify the MS of the change and release of the resource allocation using a separate resource allocation message. As a result, when using the circuit-mode resource allocation scheme, the BS has no need to transmit the resource allocation message at every frame, thereby making it possible to prevent the waste of resources caused by the transmission of the resource allocation message.
With reference to FIG. 2, a description will now be made of a resource allocation method based on a circuit-mode resource allocation scheme in an IEEE 802.16 communication system.
FIG. 2 is a diagram schematically illustrating a resource allocation method based on a circuit-mode resource allocation scheme in an IEEE 802.16 communication system.
Before a description of FIG. 2 is given, it should be noted that the IEEE communication system uses two resource allocation schemes, namely a packet-mode resource allocation scheme and a circuit-mode resource allocation scheme. Referring to FIG. 2, both a resource allocation method based on the packet-mode resource allocation scheme and a resource allocation method based on the circuit-mode resource allocation scheme are illustrated. For convenience, however, a description of the resource allocation method based on the packet-mode resource allocation scheme will be omitted herein. For convenience, resources allocated using the circuit-mode resource allocation scheme will be referred to as ‘circuit-mode resources’.
The slot numbers referred to herein and illustrated in FIGS. 2 and 3 are numbered separately for each of the packet-mode resource allocation scheme and the circuit-mode resource allocation scheme in order to simplify the explanation. The slot numbers for the packet-mode resource allocation scheme are numbered in the same direction as the resource allocation beginning with the first slot used for the packet-mode resource allocation scheme. The slot numbers for the circuit-mode resource allocation scheme are numbered in the opposite direction to the resource allocation beginning with the last slot used for the packet-mode resource allocation scheme. The slot numbers used herein are merely for the purpose of explanation and any other slot numbering scheme may equally be used, such as numbering all of the slots of a subframe. Further, the direction of the resource allocation is merely an example, as at least one of the packet-mode resource allocation scheme and circuit-mode resource allocation scheme may employ a resource allocation in a direction opposite to that described herein.
Referring to FIG. 2, when resources are allocated for UL data bursts included in a UL subframe using the circuit-mode resource allocation scheme, UL resources are allocated slot by slot beginning from a start offset. The start offset indicates a location from which the BS starts allocating UL resources using the circuit-mode resource allocation scheme, and a slot #10 is assumed to be the start offset in FIG. 2. A detailed description of the start offset will be given below.
For example, in FIG. 2, a circuit-mode resource #1 includes 2 slots in the forward direction from slot #10 which in this example is the start offset, a circuit-mode resource #2 includes 2 slots in the forward direction from slot #8 which is the next slot of the slots included in the circuit-mode resource #1, and a circuit-mode resource #3 includes 6 slots in the forward direction from slot #6 which is the next slot of the slots included in the circuit-mode resource #2.
However, the use of the circuit-mode resource allocation scheme described in FIG. 2 may cause a reduction in resource efficiency, which will be described with reference to FIG. 3.
FIG. 3 is a diagram illustrating a case where a circuit-mode resource is de-allocated in an IEEE 802.16 communication system.
Referring to FIG. 3, it is assumed that the circuit-mode resource #2 among the 3 circuit-mode resources allocated in FIG. 2 is de-allocated. It is also assumed that after the circuit-mode resource #2 is de-allocated, a circuit-mode resource #4, or a new circuit-mode resource, may be allocated. The number of slots included in the circuit-mode resource #4 is assumed to be 4. In this case, the number of slots included in the circuit-mode resource #4 exceeds the number 2 of slots included in the de-allocated circuit-mode resource #2. Therefore, the circuit-mode resource #4 cannot use the slots which were included in the circuit-mode resource #2, and should therefore include 4 new slots following the circuit-mode resource #3 that as illustrated in FIG. 3 would comprise larger slot numbers than the start offset. The slots included in the circuit-mode resource #4 include 4 slots in the forward direction from slot #14, which is the new start offset. As a result, the 2 slots of a slot #8 and a slot #7, which were include in the de-allocated circuit-mode resource #2, become a hole, and the hole is an unavailable resource.
As described in FIG. 3, the use of the circuit-mode resource allocation scheme may cause creation of the hole, impeding continuity of resource allocation. The creation of the hole reduces the resource efficiency, resulting in a decrease in efficiency of the IEEE 802.16 communication system.